Blocking iMessage Blocks Push Notifications

Author:
Luis Fernandes
December 04, 2018 17:33Updated

Summary

Due to the nature of Apple servers, blocking or throttling iMessage traffic will also have an effect on push notifications

Overview

The Exinda appliance gives administrators multiple avenues to stop or throttle applications that can use a lot of bandwidth in the network. An application that many would consider discardable or able to be easily limited in bandwidth is iMessage.

If there discarding iMessage traffic, it can be seen that all push notifications on iOS devices that have traffic going through the Exinda (ie, on wifi) will stop displaying.

Cause

Apple uses the 'Apple Push Notification Service' (APNS) in order to allow application creators to push out information to iOS devices. This includes mail servers being able to push out notifications of calendar and email, or app creators to be able to push text based messages straight to the device. iMessage, the iOS application that perform instant messaging, uses APNS as a back end. iMessage sets up a persistent connection with an iOS Server and when a user sends or receives a message, it is pushed to/from the server and then to the other party.

Because iMessage extensively uses the APNS infrastructure, the 'iMessage' classification will cover all APNS notifications. This means that if iMessage is discarded in an optimizer policy, then all APNS messages will be discarded, regardless of the application of origin. This means that email push notifications, calendar updates, etc, will not work. Likewise, throttling iMessage to an extremely small bandwidth can cause latency or drops for APNS. APNS messages are small by default (limited to 2KB) however, when combining many iOS users into a single policy based on iMessage, the bandwidth applied might not be enough.

Resolution

Remove the policy for discarding iMessage traffic or increase the bandwidth allocated to the policy.